Over the last twenty years, many contributions appeared on the relationship between working during school and academic performance using both quantitative and qualitative research methods. The obvious assumption is that a full time working student will show a lower academic performance relatively to a part time working student or a full time student. However, the empirical evidence doesn't seem to support this assumption because other variables affect the academic performance such as talent, motivation, ambition, and efficiency of studying time. We believe that the efficiency of studying time can be influenced by physical activity which paradoxically has been totally ignored in the literature. Thus, the scope of this paper is to examine the relationship between academic performance and working hours by explicitly considering the role of physical activity. (Contains 3 tables.)